1. Field of Invention
The present invention relates to the manipulation of fluid contact surfaces in vehicles for controlled actuation. More specifically, the invention relates to apparatus and methods employing a zero Poisson cellular support structure to articulate the effective control of a fluid contact surface of a vehicle.
2. Description of Related Art
Since the advent of vehicle flight, methods to obtain improved aerodynamic performance have been under consideration. The ability to maneuver a fixed wing aircraft may be limited by factors related to airfoil design, weight, and flight conditions.
Cellular structures or cellular materials are known in the design of aerodynamic components and devices. Cellular structures provide high compressive strength to weight ratios and the ability to maintain their structure using less expensive materials. For example, cellular structures may be used in the surface layer, or skin, of flight vehicles or in the core of a control surface. Generally, materials such as composite laminates, sheet metal, or foils are used to provide the lightweight yet durable structure.
One known cellular shape is a standard honeycomb. Standard honeycombs are arranged so that each side of an internal unit cell is shared by an adjacent unit cell, one per side for the six bordering unit cells. A honeycomb arrangement is coupled such that the entire honeycomb structure undergoes overall structural deformation in both the primary and transverse directions. The measurement of structural deformation is better defined using Poisson's ratio. Poisson's ratio is defined as the ratio of the negative contracting transverse strain (i.e., normal to the applied load) divided by the extension or axial strain (i.e., in the direction of the applied load). A positive Poisson's ratio indicates that a material will contract laterally when stretched, and expand laterally when compressed (i.e., an increase in length causes a decrease in width). Since typical honeycomb structures suffer a decrease in width when subject to an increase in length, they have a positive Poisson's ratio.
Auxetic structures or materials, on the other hand, are known for their negative Poisson's ratio. Auxetic structures have the opposite (negative Poisson) effect, in that they expand or contract in multiple directions simultaneously to an applied load (i.e., an increase in length causes an increase in width). Examples of auxetic structures may include certain types of foams, polymeric and metallic materials, and composite laminates. Based on their geometry and cellular arrangement, the most common honeycomb-like auxetic structures are often referred to as re-entrant honeycombs.
Generally, manufacturing techniques of honeycomb cores include corrugated processes, extrusion dies, entwining of sheet metal, welding, laser bonding, diffusion bonding, and machining foam-filled billets.
Conventional control surfaces have become commonplace in the design of aerodynamic vehicles, particularly aircraft. Historically, these devices have primarily consisted of trailing edge flaps (ailerons or elevons), leading edge devices (slots or slats), elevators, and rudders, which are rigidly fixed in their size and shape.